This invention concerns a photographic developer system comprised of two separate compositions adapted to be sequentially utilized in the treatment of photosensitive materials, and a process utilizing said developer system in the treatment of silver-based photosensitive materials capable of producing black and white pictures.
Photosensitive materials employed for photographic purposes are generally comprised of a supporting sheet such as film or paper, one surface of which is coated with a uniform layer of a hydrophilic polymer, such as gelatine, which contains an emulsion of finely divided particles of photosensitive silver compounds such as silver chloride, silver bromide and the like. When a clear film is employed as the supporting sheet, the resulting developed product will generally be a "negative" wherein portions of the photosensitive material exposed to the light of a light image are opaque, and the non-exposed portions are transparent.
The negative or "film" may subsequently be utilized in producing black and white pictures or "prints". Photosensitive material for making prints, generally referred to as printing or enlarging paper, utilizes a white paper as the supporting sheet. The emulsion coating of the printing paper is exposed to a light image formed by passing light through a negative. Upon development of the exposed printing paper, those portions struck by light will be black, and regions unstruck by light because of the occluding nature of the opaque portions of the negative, will be white. In this manner, the print will be an accurate rendition of the photographed scene insofar as light-appearing objects will appear white, dark-appearing objects will appear black, and various intermediate gradations from white to black will also be present.
In the developing process, the light exposed film or print paper is immersed in an aqueous solution of a "developer", whereupon particles of silver compound which have been struck by light are chemically reduced to black atomic silver. Developer compositions are generally comprised of an aqueous solution containing one or more chemical reducing agents and other species which modify the action of said reducing agent or provide auxilliary effects. The most generally used reducing agents are hydroquinone and phenylamines containing the chemical configuration ##STR1## Typical phenylamines include N-methyl-p-aminophenol sulfate, 1-phenyl-3-pyrazolidone and its derivatives, triaminophenols, and p-phenylenediamine. N-methyl-p-aminophenol sulfate is commercially available under various trademarks such as Metol, Elon, Photol, Verol, Rhodol, Armol, Genol and Pictol; and will hereinafter be referred to as Metol.
The use of a developer formulation comprised of Metol, hydroquinone and sodium sulfite has been disclosed in U.S. Pat. Nos. 3,265,501; 2,178,896; 3,161,513; and elsewhere. Such mixtures generally afford characteristics representing a compromise of the several features sought in a developer formulation. The combination of Metol and hydroquinone provides a synergistic effect which produces more acceptable image contrast than Metol alone. The sodium sulfite is considered to function to preserve the developer by minimizing aerial oxidation, and stabilize the developer by interacting with the oxidative byproducts of the development process.
Following development, the photosensitive material is treated with an aqueous solution, generally called fixer, hypo, or clearing agent, the primary purpose of which is to dissolve out of the hydrophilic polymer coating remaining unreduced silver compounds. The black silver remains within the coating. By virtue of said development process, areas of the photosensitive material upon which light impinged will be black. The other areas, in the case of a negative will be transparent, and in the case of a printing paper will be white.
It has long been known that, in the developing process to create negatives or prints from latent images on exposed photosensitive material, factors of time and temperature must be carefully observed. Longer durations of contact of the photosensitive material with the developer solution, and higher temperatures of said solution cause more intense developing action with consequent formation of larger quantities of silver in black form in the case of black-and-white photosensitive materials. Shorter durations of contact and lower temperatures produce lesser quantities of silver in the photosensitive material.
Securement of optimum results in the development process is particularly difficult for those who may lack extensive experience in the techniques involved or be without adequate equipment to accurately measure and control the temperature and/or time of the development process. Such difficulties are particularly encountered by students or others making initial efforts to develop photosensitive materials.
Another general problem encountered as a result of the developing process is that the black particles of silver, instead of remaining uniformly dispersed within the emulsion coating, may agglomerate. This causes a "grainy" appearance and is particularly noticeably when a negative having high "grain" is utilized to make an enlarged print using a photographic enlarger. Excessive grain in the print is objectionable because it detracts from the realistic rendition of the original scene photographed. Although developer compositions specially formulated to produce fine grain have been known, such compositions do not usually enjoy a long "shelf life", namely stability upon long term storage.
It is accordingly an object of the present invention to provide a photographic developer system which, in its action upon a photosensitive material, is relatively insensitive to variations of time and temperature.
It is another object of this invention to provide a photographic developer system of the aforesaid nature possessing a relatively long shelf life.
It is a further object of the invention to provide a photographic developer system of the aforesaid nature capable of producing black and white pictures evidencing relatively little graininess.
It is a still further object of the present invention to provide a process for the development of black and white film to produce a negative evidencing relatively little graininess.
These objects and other objects and advantages of the invention will be apparent from the following description.